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The Canon 70-300mm DO IS is the world's first consumer zoom to use Fresnel lenses. Canon uses a green band around the front to denote a DO lens. Canon call this technology "Diffractive Optics" (DO) to avoid riling up unnecessary fear in laypeople familiar with Fresnel lenses' former use only in lighthouses, theatrical lighting and projector condensers.

The Canon 70-300mm DO IS is expensive because of this new technology. It has unusually good optics in an unusually small size. However, I find the rest of the lens' design, packaging and Image Stabilization system less attractive than other lenses, like the half-as-expensive non-DO version, as I explain at the end under Recommendations.

Good News:

1.) Short.

2.) Smooth and quiet auto and manual focus.

3.) Quite free from color fringes.

4.) Less distortion than similar range lenses at 70mm.

Bad News:

1.) Image Stabilization not good enough to give consistently perfect hand-held shots at 300mm at ISO 100 in daylight. The similarly priced Canon 70-200mm f/4L IS and half-priced Canon 70-300mm IS are much better.

7.) Slow aperture. In actual use it's closer to f/5.6 throughout most of the zoom range than it is to f/4.

Technology

The Canon 70-300mm DO IS uses a sandwich of Fresnel (sawtooth cross section) surfaces so there's nothing to collect dust or cause weird flare problems.

Concentric Fresnel Lines in the Canon 70-300mm DO IS (the spiderweb-like lines in the glass, not the ribbed black plastic behind it)

Augustin Jean Fresnel (1788 - 1827) invented the basis of this technology in 1822. He realized you could collapse a lens like a collapsible drinking cup, but unlike the cup, the lens would work the same but without all the glass and weight.

Canon perfected it for use in photographic optics, and if you look at reflections of objects around you in the front element (not shown above), you can see that Canon has created the equivalent of an extremely thick, heavily curved element whereas in fact there isn't one. This allow the use of extremely low dispersion glass, which also has a low refractive index. The low dispersion reduces color fringes, but the low refractive index also require thicker, more heavily curved elements.

Canon has done such a great job of bringing this technology to photography that it's almost impossible to see the rings. To see them in the photo above I had to shine the sun at just the right angle to highlight them. I saw no other effects in actual photography, just the benefits of getting the optical equivalent of a highly curved aspherical surface without the weight or former expense.

EF: Electronic Focus. All modern Canon lenses focus with a motor in the lens.

DO: Diffractive Optics, which is Canon's name for Fresnel lenses, previously only used in projector light condensers.

IS: Image Stabilization, which means no tripod needed except at night. See Why IS Matters.

USM: Ultra-Sonic Motor: The focus motor operates silently.

Focal Length: 70-300mm. Used on a 1.3x camera it gives angles of view similar to what an 88-377mm lens would give on a 35mm film camera. On a 1.6x camera it gives angles of view similar to what an 114-486mm lens would give on a 35mm film camera.See also Crop Factor.

The focus is fast and direct on my Canon 5D. It's almost as good on my Rebel XTi, but not always as accurate.

What Moves: Nothing, focus is internal.

Focus Distance Scale: Yes.

Depth of Field Scale: NONE.

Speed: AF speed, like almost everything else today from Canon, is faster than my own eyes.

Sound and Noise: Autofocus is almost silent.

Ease of Manual Focusing: Excellent, just grab the ring at any time, no need to move any switches. Unlike the zoom ring, manual focus is geared to be slow. Manual focus is very precise at 300mm, but might be a little too slow (but very precise) at 70mm.

Autofocus Accuracy

The good news is that it's always dead-on on my 5D, even wide open. I can get out-of-focus shots where the AF system simply makes mistakes on my Rebel XTi. If you use one of these on a Rebel, be sure it focuses accurately enough for you. It's fast, but sometimes misses on my Rebel XTi.

Focus Breathing

None.

Focus breathing is a motion picture term which refers to what happens as you pull (change) focus from near to far. I list this for people putting these lenses on their Canon XL-1s for shooting video.

The Canon 70-300mm DO IS could be a real winner for cinematography, since I see no focus breathing.

Bokeh is good. Backgrounds are quite pleasant and undistracting. Canon never ceases to impress me, since I'm used to bad Bokeh from my aspherical Nikon lenses. Bokeh appears to be something which Canon rolls into the design equations, and Nikon doesn't, for their zooms.

Falloff, or the corners getting dark, is a little better than average. There is the usual falloff wide open at the long end, and it's very mild everyplace else.

Here are shots of an Expodisc with my full-frame 5D. This would be completely invisible on a 1.6x camera. (see crop factor.)Shooting flat fields and laying them on another flat field exaggerates even the slightest falloff. You'll never see it this bad in normal photography.

I haven't been able to get the Canon 70-300mm DO IS to flare. Here are shots against a strong backlight.

Auto Exposure

+2 stops

+5 stops

Even at +5 stops, everything looks fine when shot into the bright light.

As an extreme example, I had a blind friend point the lens and my Rebel XTi at the mid-day California sun, overexpose and put a tree in the side to help highlight any ghosts that might appear. (He used to be sighted, but made too many of these shots himself. Don't do this!)

This is the worst I could make it look, and if this was exposed correctly, even then probably would have looked OK. Lenses rarely flare anymore, just as the electronic shutters of the past 20 years have never erred from a set shutter speed.

Worst possible forced example of ghosting, 70mm at f/11.

Note the old-fashioned hexagon shapes, which come from the six-bladed diaphragm.

The crop factor of a 1.6x camera like my Rebel XTi lets it get a closer crop from the same distance:

at closest focus at 300mm, f/8, full image, Canon Rebel XTi.

100% crop from above, no extra sharpening.

I had to play around to get it this good. The Canon 70-300mm DO IS tended to focus behind my intended subject at 300mm and close distances, so I had to focus by trial-and-error. Get a real macro lens if this is important to you.

The Image Stabilizer sounds like there is a motor spinning something around inside the lens. I even can feel it as it runs! It feels and sounds like an old Intermatic timer.

There is a clicking when when you tap the shutter and IS turns on, and another click as it turns off. This is normal and the way almost all of my IS and Nikon VR lenses sound. The guts of the lens are wiggling around to counteract our own hand vibration.

I dislike the way in which the Canon 70-300mm DO IS zooms. This, and my inability to get consistently sharp shots at 300mm without camera-shake induced blur, are my two biggest complaints with this lens.

The wide zoom range is cramped too close together on the zoom ring, making precise zooming difficult. See how the range from 70 to 300mm doesn't takes only half the visible width of the ring? I'd greatly prefer it to be spread further out across the zoom ring. This would make it easier to turn and more precise for setting exact compositions.

It is unbalanced, meaning it's easier to zoom to longer focal lengths when pointed down and easier to zoom to shorter focal lengths when pointed up. Point the Canon 70-300mm DO IS the other way and it's difficult to turn the zoom ring because you're pulling the front of the lens up against gravity.

Because of this I need to dedicate at least two fingers of my left hand for zooming. I greatly prefer the superior zooming of the similarly priced Canon 70-200mm f/4L IS, which is so smooth, spread out and well balanced that I can zoom it with one finger of my right hand, allowing one-handed shooting. I need both hands with this 70-300mm DO IS.

Zoom Creep

The zoom on my new sample was on the stiff side, so I didn't have any creep issues. There is a lock at 70mm which I never needed to use.

Focus Shift while Zooming

Focus shifts very little. You usually can get away without refocusing after zooming, which is better than most zooms. Of course this will vary from sample to sample and camera body to camera body.

Actual Focal Lengths

Seeing how the Canon 70-300mm IS (not DO) gives a bigger image at 4.9' and 300mm than this lens does at 300mm and 4.6' makes me suspect that the internal focusing system of the 70-300mm DO IS is not giving the equivalent of 300mm at the closest distances.

You'll get the same magnification at infinity, but the more traditionally designed Canon 70-300mm IS (not DO) gives greater magnification up close.

Maximum Aperture

This is a slow lens. It's closer to f/5.6 throughout most of the range than to f/4.

70mm: f/4.5

100mm: f/5.0

135mm: f/5.0

200mm: f/5.6

300mm: f/5.6

Focal Length Encoding Accuracy

The EXIF data agrees with the settings marked on the lens at 70, 100, 135, 200 and 300mm.

I have not correlated the accuracy of the markings with actual focal lengths.

The Canon 70-300mm DO IS is interesting to collectors as being the world's first Fresnel (DO) consumer zoom, but I prefer other lenses that cost less. You're paying a premium for gee-whiz technology and superior focus flexibility over the non-DO Canon 70-300mm IS, as well as losing 1.7" (43mm) in length, but otherwise I prefer the non-DO version at half the price.

The non-DO Canon 70-300mm IS has superior image stabilization and therefore overall image quality. The only thing you lose for half the price is dorky manual focus, and a focus ring which moves during autofocus. The IS works much better on the less expensive lens at 300mm where it's needed most, and the less expensive lens is 3 ounces lighter. I see no point in paying twice as much for the DO which is more difficult to zoom just to lose 1.7" (43mm) in length. They are the same maximum diameter.

For the same price as this DO lens, the Canon 70-200mm f/4L IS is superior if you don't mind missing the 300mm range, which doesn't work that well on the DO lens anyway hand-held. Everything else about the 70-200mm f/4L IS is superior.

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